Current and proposed future vehicle fuel vapor emission standards continue to stimulate new proposals and designs for the control, storage and disposal of fuel vapors. These vapors include both those normally displaced out of the tank to atmosphere as fuel enters the tank, the so called fuel fill losses, and pressurized fuel vapors that are naturally formed in the tank, and which escape as soon as the gas cap is removed, the so called puff losses. Such designs are now reflected in the issued U.S. patents, designs which are now beginning to be modified and improved.
An example is found in U.S. Pat. No. 4,630,749 to Armstrong et al, assigned to the assignee of the present invention. As disclosed there, the lower part of a housing opens through the filler neck below a swinging flapper door near the top of the filler neck, which is pushed open by the insertion of the fuel nozzle. A vent line from the top of the housing runs to a standard vapor storage canister. The inserted nozzle passes through a wiping seal, blocking the normal vapor exit path to atmosphere. Vapors can instead exit only through the housing and vent line to the storage canister. One desired function of such a vent means is that the vent line should be closed off at times other than during the fuel fill process. To accomplish this, a first ball valve within the housing is continually spring loaded down to close off the exit path. The ball valve is pushed up by a finger on the flapper door as it is pushed open, compressing the spring, and opening up the exit path. Another desired function is that the vapor exit path should be automatically shut off in the event that liquid fuel rises to the level of the housing, so that raw fuel does not reach the storage canister. This is accomplished by the provision of a second, buoyant ball valve, which floats up at the upper interior of the housing to shut off the exit path if liquid fuel reaches it enters. While the use of a second ball valve inevitably take greater volume than would just one, the first ball valve cannot also serve as a shut off, since it is immobilized between the flapper door and the compressed spring and cannot float freely.
It is known, in general, to make a single ball serve both the close off function before fuel fill, and the automatic shut off function during fuel fill. This may be done by using a lever extension on the flapper door, or some other retention structure that is released by the removal of the gas cap, to hold a buoyant ball valve up against a seat. Then, upon removal of the gas cap, or upon insertion of the fuel nozzle through the flapper door, the buoyant ball falls down under its own weight to a lower position below the seat, opening up the vapor venting path to the canister. Should liquid fuel rise that high, then the buoyant ball can float up to shut off the exit path. An inevitable limitation of such systems is that, since the ball is very light, gravity does not provide a great deal of force to pull it down off of the seat. Consequently, the stickier and more effective seat surfaces cannot be used, at least not without some additional mechanism to kick the lightweight ball off of the upper seat as the nozzle is inserted to assure opening of the vapor path.